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参数资料
| 型号： | LTC3615EUF#PBF |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, PQCC24 |
| 封装： | 4 X 4 MM, LEAD FREE, PLASTIC, MO-220WGGD, QFN-24 |
| 文件页数： | 18/32页 |
| 文件大小： | 585K |
| 代理商： | LTC3615EUF#PBF |
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LTC3615/LTC3615-1
25
3615fa
Design Example
As a design example, consider using the LTC3615 in an
application with the following specications:
VIN = 3.3V to 5.5V
VOUT1 = 2.5V
VOUT2 = 1.2V
IOUT1(MAX) = 1A
IOUT2(MAX) = 3A
IOUT(MIN) = 100mA
f = 2.25MHz
Because efciency is important at both high and low
load current, Burst Mode operation will be selected by
connecting the MODE pin to SGND.
First, calculate the timing resistor:
R
EHz
MHz
k
RT SYNC
/
.
==
411
225
178
Ω
Next, calculate the inductor values for about 1A ripple
current at maximum VIN:
L
V
MHz
A
V
1
25
225
1
25
55
0
=
=
.
–
.
.6
6
2
12
225
1
12
55
μH
L
V
MHz
A
V
=
.
–
.
= 042
.μH
Using a standard value of 0.56μH and 0.47μH inductors
results in maximum ripple currents of:
ΔI
V
MHz
μH
V
L1
25
225
0 56
1
25
55
=
.
. .
–
.
=
108
12
225
0 47
1
2
.
. .
–
A
I
V
MHz
μH
L
Δ
..
.
2
55
089
V
A
=
COUT will be selected based on the ESR that is required
to satisfy the output voltage ripple requirement and the
bulk capacitance needed for loop stability. For this design,
47μF ceramic capacitors will be used with X5R or X7R
dielectric.
CIN should be sized for a maximum current rating of:
I
II
A
RMS MAX
OUT
RMS
() =+
=
12
22
2
APPLICATIONS INFORMATION
where the LTC3615 is running at high ambient temperature
with low supply voltage and high duty cycles, such as in
dropout, the heat dissipated may exceed the maximum
junction temperature of the part. If the junction temperature
reaches approximately 160°C, all four power switches
will be turned off and the SW node will become high
impedance.
To prevent the LTC3615 from exceeding the maximum
junction temperature, the user will need to do some thermal
analysis. To determine whether the power dissipated
exceeds the maximum junction temperature of the part.
The temperature rise is given by:
TRISE = PD θJA
where PD is the power dissipated by the regulator, and
θJA is the thermal resistance from the junction of the die
to the ambient temperature. The junction temperature,
TJ, is given by:
TJ = TA + TRISE
where TA is the ambient temperature.
As an example, consider this case: the LTC3615 is in
dropout at an input voltage of 3.3V with a load current for
each channel of 2A at an ambient temperature of 70°C.
Assuming a 20°C rise in junction temperature, to 90°C,
results in an RDS(ON) of 0.086mΩ (see the graph in the
Typical Performance Characteristics section). Therefore,
the power dissipated by the part is:
PD = (I12 + I22) RDS(ON) = 0.69W
For the QFN package, the θJA is 37°C/W.
Therefore,thejunctiontemperatureoftheregulatoroperating
at 70°C ambient temperature is approximately:
TJ = 0.69W 37°C/W + 70°C = 95°C
Notethatforverylowinputvoltage,thejunctiontemperature
will be higher due to increased switch resistance RDS(ON).
It is not recommended to use full load current at high
ambient temperature and low input voltage.
To maximize the thermal performance of the LTC3615, the
Exposed Pad should be soldered to a ground plane. See
the PC Board Layout Checklist.
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